Optical receiver modules used for receiving high speed—GHz-optical data signals propagating along an optical fiber are known to those of skill in the art. Typically within these optical receiver modules there is an optical detector electrically coupled to an amplifier circuit in such a manner that light from the optical fiber illuminates the optical detector, the optical detector generates photocurrent in response thereto, and the amplifier circuit amplifies this photocurrent. The optical qualities of the optical detector are typically determined at least in part by the material structure of the optical detector. For some ranges of wavelengths, the materials of choice for the optical detector are costly, and as such, semiconductor materials used for manufacturing the amplifier circuit and the optical detector are typically not the same. Thus, the prior art optical detectors must be electrically wired to the amplifier circuits using wires in order to conduct the photo current.
Typically, the amplifier circuit and the optical detector are purchased from third party vendors prior to assembly. Thereafter, the optical detector, the amplifier circuit, decoupling capacitors, and a module housing are assembled to form an optical receiver. Typically, the housing is designed for easy coupling to an optical fiber. Unfortunately, since these modules are used for receiving high speed optical data, the length of bond wires used to connect the optical detector to the amplifier is critical. These wires exhibit inductance and as such, when photocurrent levels are extremely small in the order or microamperes, variations in intensity of the high speed optical data may not be representative of the actual data transmitted due to the effects of these bond wires. Thus, the module may be more or less sensitive depending on an exact configuration and manufacture.
In manufacturing, manufacturers typically are unable consistently to achieve optimal optical operating characteristics for the assembled receiver modules because the wires coupling the detector to the amplifier circuit play an important role in the performance of the receiver module and are known to vary significantly in manufacture.
Furthermore, isolated testing of the amplifier circuit is not economical or effective without the optical receiver coupled thereto due to the frequency range of operation of the device. Thus, even when optimally assembled, the module may fail to meet desired performance characteristics due to amplifier shortcomings.
Finally, the performance of the module or some subset of the entire assembly will also be dependent upon the value, position, and performance of the power supply decoupling capacitors. These capacitors are often integrated into the module by the manufacturer and contribute to the difficulty of designing a manufacturable module.
As a result a need therefore exists to manufacture the receiver module in such a manner that facilitates testing of the receiver module as a complete system in order to eliminate effects that yield undesirable performance prior to selling thereof. Unfortunately, due to the costly nature of many of the optical receiver semiconductor materials, integration of the module into an integrated circuit format is not considered practicable. For example, different material processing systems commonly rely on wafers having different sizes. Thus, a same wafer mask is not usable with the different processes. This greatly increases the design and manufacture costs for implementing a fully integrated or monolithic photodetector with amplifying circuit.
It is therefore an object of the invention to provide an optical receiver module and method of testing thereof that provides improved performance and performance consistency of the optical receiver module finished product.